To the best of my knowledge, George Washington never explicitly offered his opinion of the First Amendment. It was proposed by Congress and ratified by the states during his first term as president but, per the Constitution, without his formal participation. Washington wrote to James Madison privately on May 31, 1789, stating, “I see nothing objectionable in the proposed Amendments. Some of them in my opinion, are importantly necessary; others, though of themselves (in my conception) not very essential, are necessary to quiet the fears of some respectable characters and well meaning men.”
The Constitution’s abolition of religious tests for office emancipated American Jews and Catholics from legal disabilities at the federal level, and decades before Britain did the same (this was only seven years after the devastating anti-Catholic Gordon Riots in London).